What does "Received SIGUSR1 or SIGINT" mean? - Tools

This is a discussion on What does "Received SIGUSR1 or SIGINT" mean? - Tools ; I am getting errors with "Received SIGUSR1 or SIGINT".
I do what to fix the errors but I have no idea what "Received SIGUSR1 or
SIGINT" even means.
Also, why would rsync report no space available when using -X when ...